(a) Field of the Invention
The present invention relates to a polyarylene-based polymer, a preparation method for the same, and a polymer electrolyte membrane for a fuel cell using the polymer.
(b) Description of the Related Art
A fuel cell is a device that converts chemical energy into electrical energy through an electrochemical reaction of a fuel such as, for example, hydrogen or methanol, with oxygen, air, or another oxidizing agent. The fuel cell comprises electrodes (i.e. an anode and a cathode) and an electrolyte membrane disposed between the two electrodes. This basic construction is called the “membrane-electrode assembly”. The role of the polymer electrolyte membrane is to provide a means for transporting protons derived from the anode to the cathode (requiring high proton conductivity), and for separation of the anode from the cathode (requiring high dimensional stability against hydration and low methanol permeability).
The polymer electrolyte membranes (PEMs) are broadly classified into fluorinated PEMs and hydrocarbon-based PEMs. The hydrocarbon-based PEMs are prepared using polymers such as, for example, polyimide (PI), polysulfone (PSU), polyether ketone (PEK), polyarylene ether sulfone (PAES), and the like, and are generally superior to the fluorinated PEMs in terms of their low production cost and good thermal stability.
To achieve proton conductivity comparable to the level of fluorinated PEMs, hydrophilic ionic groups such as sulfonic acid groups, or the like, are introduced into the hydrocarbon-based PEMs. Unfortunately, the addition of such hydrophilic ionic groups causes an excessive swelling of the membrane with water, which deteriorates the mechanical properties and stability of the membrane and causes leakage of the sulfonated resin.
In an attempt to solve this problem, it has been proposed to introduce covalent cross-links to the resin to lower the water solubility of the electrolyte membrane, thereby inhibiting leakage of the resin. It has also been proposed to introduce sulfonic acid groups onto the side chains of the polymer, rather than the main chain, to increase the fluidity of the polymer chain and enhance the proton conductivity.
Unfortunately, the hydrocarbon-based PEMs are currently not well suited for commercial use in fuel cells because they suffer from several major drawbacks. For example, hydrocarbon-based PEMs have low proton conductivity. Additionally, it is difficult to synthesize the high molecular weight polymers with covalent cross-links and to then prepare a polymer membrane using the synthesized polymers. Another difficulty is caused by a rise of the glass transition temperature Tg, which causes the fluidity of the polymer to decrease, thereby resulting in the membrane having poor mechanical properties.